READ ( UNIT = TRIM(String),...

[Jerry DeLisle]

Philippe Schaffnit wrote:
> Hi!
> 
> I was trying to iron out a wrinkle from a piece of code, when I stumbled
> onto something which I find quite surprising, what I hold to be a
> 'reject valid' from GFortran: the 'reject valid' would belong here, the
> other bit probably not, but if a kind soul could nevertheless enlighten
> me, I would greatly appreciate it!
> 
> Take the following piece of code:
> 
> !
>       PROGRAM Test
> !
>       IMPLICIT NONE
> !
>       INTEGER                 ::   Number, IO_Stat
> !      CHARACTER ( LEN = 250 ) ::   String = "Hello world!"
>       CHARACTER ( LEN = 250 ) ::   String = "/Hello world!"
> !
> !      READ ( UNIT = TRIM(String), FMT = *, IOSTAT = IO_Stat ) Number
>       READ ( UNIT = String, FMT = *, IOSTAT = IO_Stat ) Number
>       WRITE ( UNIT = 6, FMT = * ) Number, IO_Stat
> !
>       END PROGRAM Test
> !
> 
> The obvious one first: "GNU Fortran (GCC) 4.3.0 20071026 (experimental)
> [trunk revision 129646]" rejects "READ ( UNIT = TRIM(String)," with 
> 
> READ ( UNIT = TRIM(String), FMT = *, IOSTAT = IO_Stat ) Number
>                   1
> Error: UNIT specification at (1) must be an INTEGER expression or a
> CHARACTER variable
> 
> Is this warranted by the standard?, I would expect it to be fine: the
> SGI, Lahey and Sun compilers seem happy with it... (for the record, the
> Intel one doesn't either)
> 
> Now for the really weird part, if I remove the 'TRIM' to get over this,
> I would expect an IO error to be raised, but I have yet to find a
> compiler which does!
> 
The slash is considered a value separator. The value is read until a separator 
is found.  Right from the standard, 10.8:

  A value separator is

(1)   A comma optionally preceded by one or more contiguous blanks and 
optionally followed by one or more contiguous blanks,

(2) A slash optionally preceded by one or more contiguous blanks and optionally 
followed by one or more contiguous blanks, or

(3) One or more contiguous blanks between two nonblank values or following the 
last nonblank value, where a nonblank value is a constant, an r∗c form, or an r 
form.

If you try to read a second value in that READ statement you will get the 
expected error.

       CHARACTER ( LEN = 250 ) ::   String = "/Hello world!"

       READ ( UNIT = String, FMT = *, IOSTAT = IO_Stat ) Number, number

Regards,

Jerry